Selection of Brain Metastasis-Initiating Breast Cancer Cells Determined by Growth on Hard Agar

Abstract

An approach that facilitates rapid isolation and characterization of tumor cells with enhanced metastatic po-The vast majority of cancer deaths result from progressive growth of metastases that are resistant to conventional therapies. 1 Metastases originate from a selected subpopulation of cells that reside in a biologically heterogeneous primary tumor. 2,3 Results from experimental 4 and clinical 5 examinations indicate that most metastases are clonal in origin and that the metastatic process is highly selective. 6 Studies have also shown profound differences between local and disseminated cancers, 7 suggesting that information on primary tumors alone may not be sufficient to determine optimal therapeutic interventions. For this reason, researchers have directed considerable effort toward improving understanding of the molecular phenotypes of metastasis-initiating tumor cells.One widely used experimental approach to isolate populations of tumor cells with enhanced metastatic potential is an in vivo selection process in which tumor cells are implanted into syngeneic or immunodeficient mice and metastasis is allowed to occur. Tumor cells from the resultant metastatic lesions can be isolated and expanded to establish cell sublines, some of which may have higher metastatic capacity than the parental tumorcell population. 8 Comparative gene expression profiling of parental tumor cells and their metastatic subpopulations has yielded invaluable information regarding the genetic determinants critical for organ-specific metastasis. 9 For example, Kang et al 10 compared the transcriptional profiles of parental MDA-231 human breast cancer cells with those of a bone-colonizing variant of this cell line and reported the underlying gene expression signature required for organ tropism to bone. Investigators used a similar approach to identify genes whose expression is critical for metastasis of breast cancer cells to the brain 11 and lungs. 12 Nevertheless, although this in vivo selection technique has provided new insight into the cellular and molecular mechanisms that control site-specific metastasis, there are some disadvantages. Perhaps the principal drawback of in vivo selection is that it can be time-consuming,

The Biology of Brain Metastasis

“…Additional experiments confirmed that the growth capacity of human tumor cells on hard agar correlated with their metastatic potential in vivo (37 ). Plating GI-101A human breast cancer cells on 0.9% agar has recently been shown to select for the subpopulation of metastasis-initiating cells (38 ). The agar-selected cells, designated GI-AGR, were 5 times more invasive than the parental GI-101A cells.…”

“…The molecular phenotype of GI-AGR and GI-BRN cells was consistent with that of cancer stem cells and the basal subtype of breast cancer. Both the in vitro and in vivo selection processes were found to enrich for the population of breast cancer cells that coexpressed CD44 and CD133 (38 ). Ninety percent of the GI-AGR and GI-BRN breast cancer cells growing in cell culture conditions coexpressed CD44 and CD133, and both of these proteins were expressed in GI-101A experimental brain metastases.…”

Characterization of different CTC subpopulations in non-small cell lung cancer

“…ALDH1 is thus of interest as a metastasis initiating factor expressed in CTCs. Others have shown that CTCs in breast cancer, which express stem cell factors are able to initiate metastatic outgrowth252627. Furthermore, EGFR is discussed to be involved in the process of EMT and drug resistance and is also expressed on the metastatic initiating CTCs2829.…”

A 3D Fibrous Scaffold Inducing Tumoroids: A Platform for Anticancer Drug Development

“…Others have shown that deprivation of glutamine [61] or culturing cells on hard [62] and soft agar [63] resulted in selection of highly adaptable metastatic cancer cells. These reports suggest that the topography of 3P scaffolds may be forcing a selection of structural adaptability, potentially promoting EMT, cancer stem cell-like features and chemotherapy resistance.…”